The BMW 540i handling can be
dramatically improved by replacing the front and rear swaybars with stiffer ones.
A cost-effective approach is to use M5 parts which cost only slightly more
than $300. Depending on your 540i
model, the existing front swaybar diameter is either 24.5mm or 25mm (Sport
and 6-Speed). The rear swaybar diameter ranges from 13mm to 15mm
depending on model year and options. The M5 front and rear swaybars
are 27mm and 16.5mm in diameter, respectively. If you
don't mind spending three times as much money, Dinan offers 28mm front and 17mm rear
swaybars.

Replacing the rear swaybar on a BMW 540i is a
simple procedure that should take 30 minutes or less. However, the
front swaybar is between the engine and subframe and is significantly more
challenging.
With two people, following the
instructions below, it should be about a three hour job. With one
person, the time required will more than double, since there are several
operations that benefit from two people working together. Zeckhausen
Racing does not recommend attempting this modification solo. A
professional mechanic with a lift should be able to complete the job in
about three or four hours.

While the M5 rear
swaybar will bolt on to a 525i, 528i, or 530i, the front swaybar will
not. The front subframe on 6-cylinder models is a different
design. Thus, the M5 front swaybar can NOT be
installed on any 6-cylinder model. For these models, you need an aftermarket solution for the front swaybar, such as
Eibach or Dinan. However, all of these
6-cylinder models will benefit from the addition of the M5 rear bar, if you
are trying to reduce understeer. The rear swaybar installation is
trivial and is probably the best $140 you can spend on improving your car's
handling.

Zeckhausen Racing does not sell the parts required for this
modification. We recommend
Tischer BMW, since their pricing is outstanding and they are easy to
order from on-line.
Prices shown below are subject to change without notice and were accurate as
of April 28, 2011.

Working on your own car can be dangerous. Even quality jack stands can
collapse if not positioned properly, and a floor jack can fail suddenly and
without warning. You can be seriously injured or even killed if you do not
follow proper safety procedures. Zeckhausen Racing LLC assumes no
liability expressed or implied for the improper installation or use of these
components.

Front Swaybar Upgrade Instructions:

Jack the car up in the front as high as
possible by positioning the cup of your floor jack in the center of the
cross member located just behind the engine. Be careful not to crush
the aluminum strap that holds the rear of the plastic belly pan. It
may be necessary to drive the car onto a couple pieces of wood or a ramp
first, in order to gain enough clearance for a typical floor jack to
slide underneath from the front.

Place jack stands under the two plastic jacking blocks on the bottom of
the rocker panel, located just behind the front wheels. Gently lower the car onto the stands. Keep
in mind the car will move several inches backwards as the jack is
lowered, so be prepared to re-position the stands as you lower the
floor jack.

I can't emphasize enough how
important it is to raise the car as high as possible. When
the swaybar is being removed, it will require all sorts of twists and
turns of the bar to clear the subframe and, if the car is too low, the end
of the bar will dig into the ground, restricting your flexibility at
removing it. You may even wish to place a board underneath your
floor jack in Step 1 in order to gain another inch or two of lift.

Using a 17mm socket,
remove the front wheels. If you do not have an air wrench,
have an assistant step on the brake pedal while you remove the wheel
bolts.

Using a large Philips screwdriver, loosen
the fasteners that hold the large plastic panel under the engine.
These fasteners are 1/4 turn only and should NOT be removed from the
plastic panel. Remove panel and set aside.

Using a 15mm socket and a 15mm wrench,
remove the bolt and nut holding the idler arm (passenger side) to the sub
frame.

Idler Arm

Remove three 15mm bolts and nuts holding
the steering gear box (driver's side) to the sub frame. One vertical
bolt and another horizontal bolt are easy to remove. The forward
most vertical bolt is a challenge, since the nut is on top of the steering
box and is very difficult to access. This is where the stubby 15mm
wrench comes in handy. Work the wrench onto the nut and then loosen
the bolt with your 15mm ratchet. It can be done, but requires
patience and small hands. An assistant can see the nut from the
engine compartment above and help guide the wrench. Alternatively,
if you have a 15mm socket and at least 18" of extensions, you can
easily loosen this nut from above.

Steering Gear Box

Just forward of the driver's side engine
mount (within 2") is an 8mm
sheet metal screw that holds the power steering line bracket to the
subframe. Remove this screw.

Disconnect the ends of the sway bar, using a
16mm socket to loosen the nut and a 16mm open end wrench to prevent the
stud from turning. You may need to grind a 16mm wrench to make it
thin enough to fit.

Remove the two "C" brackets holding the sway bar
to the subframe. Use a 13mm deep well socket to remove the two nuts
holding each bracket. Pull off the two
rubber swaybar bushings.

The threaded studs are easily damaged during
the subsequent steps. To prevent this, reinstall the nuts you
removed in the previous step in order to protect them.

If your BMW came from the factory with Xenon
headlamps, you have auto-leveling sensors on the right front
and right rear suspension. Before proceeding to the next step, you
must disconnect the linkage connecting the front level sensor to the lower
wishbone. Using a 10mm open end wrench to keep the threaded stud
from spinning, remove the nut with a 10mm socket. Pull the linkage
away from the sensor arm and reinstall the nut a few turns, by hand, so it
won't be misplaced.

Diagram and photo of Xenon headlamp
auto-leveling sensor

Two aluminum control arms are connected
to the bottom of the subframe. The forward arm is called a
"wishbone" and the rear arm is called a "traction strut." Both of
these must be disconnected from the subframe and pushed out of the
way.

Wishbone

Traction Strut

The wishbone is held in place by a 16mm bolt
with an 18mm nut. Remove the nut and bolt. Pay attention to the orientation of the
bolt as you remove it. The threads face the front of
the car for some models and the back of the car for others.
A Sharpie laundry marking pen is useful to label the bolt so you don't
forget which way to put it back.

The traction strut is held in place by a
21mm bolt and nut. You will need to rotate the swaybar in order to
gain access to the head of the bolt. Remove the nut and bolt using a
21mm socket and a 21mm stubby wrench. Once the nut is removed, it
may be necessary to use a small socket extender to push the bolt all the
way through the traction strut end before you can remove it. Pay
attention to the orientation of the bolt. The threads face the
rear of the car.

Remove the left and right heat shield from
the rear of the sub frame. They are held in place with 8mm self
tapping screws. Move them away from the car so you don't
accidentally damage them. They are fragile.

After you remove the heat shields, a
collection of wires, protected by black flex tubing, and a bracket with
sharp edges will be left dangling in your face. These should also be
pulled off the back edge of the subframe, leaving them hanging at least 8"
down. It's helpful to temporarily secure these with a cable tie or a
piece of wire.

Remove the 13mm nuts holding the engine
mounts to the sub frame. There are two nuts per mount.

Place a piece of wood on the saddle of your
jack to spread the force across a wider area and to gain a few more inches of height. Place the jack under the
flat part of the engine oil pan and lift several inches until the engine mounts clear the subframe.
Be careful that the mounts don't catch on the subframe, as they might
tear. A prybar is helpful to coax the engine mounts and subframe
apart. This is where it really helps to have an assistant.

Remove the six 18mm bolts that hold the sub
frame to the chassis. The front four bolts are easily accessed.
The rear two bolts are hidden beneath plastic panels which must be pulled
back to gain access. Several 8mm sheet metal screws and a couple of
Phillips plastic screw/push rivets must be removed in order to gain access
to the rear subframe bolts. Once all the bolts are removed, the
subframe will not fall on you, but it will drop down a couple of inches.
Protect your face. (Optional: Leave the center two bolts
installed, but only engaged a few turns. This will make it easier
to align the subframe when reinstalling and will limit how far the
subframe drops.)

Work the swaybar out on the passenger side
by rotating it and pushing it until it can be slipped completely free.
This will take some time and it's the point where you will be thankful
you raised the car as high as possible. You may need to have
your assistant move
the steering wheel in order to get the bar to clear everything.

Work the new swaybar into place. For
some reason, this is easier if you start from the driver's side.

Push the subframe back up and insert the
front four bolts first, turning them by hand to be sure they are not
cross-threaded. Be careful not to pinch the power steering fluid
line between the subframe (driver's side) and the chassis.

Tighten the front four subframe bolts first,
before inserting the two rear bolts. The subframe bolts should all
be torqued to 57 lb-ft (77 N-m).

Reinstall the plastic rivets and Phillips
screws as well as the 8mm sheet metal screws that hold the plastic fender
liners and rocker covers in place.

Have an assistant gently lower the engine
back down, making sure the engine mount bolts are aligned with the holes
in the subframe. A short or medium pry bar may be used to line the
engine up with the engine mounts as it is lowered.

Install the four 13mm nuts under the engine
mounts and tighten to 18 lb-ft (24 N-m) of torque.

Reattach the traction struts to the subframe
mounts. It is easier to line this part up and get the bolt
reinstalled if your assistant turns the steering wheel for you.
Remember, the threaded end of the bolt faces the rear of the car.
Attach the nut to the bolt finger-tight but DO NOT TORQUE at this point.
The traction strut and wishbone hardware must be torqued with the car at
resting height, otherwise the bushings will tear apart in just a few
thousand miles.

Reattach the wishbones to the subframe
mounts. Insert the bolt with the threads facing forward and tighten
the nut finger-tight only.

Install the new rubber bushings on the
swaybar and then press the U-shaped bracket into place, making sure the
bump on the bushing is aligned with the hole on the bracket. Install
and tighten the 13mm nuts (two per side) on the bracket. If you are
using the factory rubber bushings, you should not apply any grease to
them.

Rotate the swaybar around so that you can
reattach the end links. Use a 16mm open end wrench to keep the
threaded end link stud from rotating and use a 16mm socket to tighten the
nut and hold the swaybar end in place.

Reattach the steering box with the three
15mm bolts and nuts. It will be just as hard to install the nut on
the vertical bolt toward the front as it was to remove it in step 6.
Be patient and use a stubby 15mm open end wrench to hold the nut in place
once you have thread the bolt into it. Alternatively, you can use a
15mm socket and at least 18" of extension to reinstall this nut from
above. Use a magnetic socket or two sided tape to hold the nut into
the socket while you lower it past the power steering hoses.

Reattach the power steering line bracket
with the 8mm sheet metal screw.

Reattach the idler arm with the 15mm bolt
and nut.

Install the two heat shields, using the 8mm
sheet metal screws.

If your car has Xenon headlights with
auto-leveling, reconnect the sensor linkage you disconnected in Step
11.

Hold the plastic panel under the engine and
tighten the metal screws 1/4 turn to fasten them.

Place a floor jack under the driver's side
shock absorber and raise the suspension until the car just begins to lift
off the jack stand.

Tighten the driver's side wishbone chassis bolt to 58
lb-ft (79 N-m) and the traction strut chassis bolt to 81 lb-ft (110 N-m).
(Remember, the wishbone is the shorter, straight arms while the traction
strut is S-shaped.) This tightening must only be done while
the suspension is compressed with the floor jack. If it is done with
the suspension dangling, the bushings will be torn apart within a few
thousand miles of driving.